Obesity worsens outcomes in all breast cancer subtypes

Obesity appears to exert a negative effect on survival of women with breast cancer regardless of subtype, according to the results of a systematic review and meta-analysis.

Out of 10,703 studies initially identified, 27 met the eligibility criteria—21 were observational and six were interventional. All six interventional studies had >5 years of follow-up and larger sample sizes (from 1,250 to 8,381).

All studies used body mass index (BMI) to describe body size, with the majority (19 studies) using BMI ≥30 kg/m² to define obesity; eight reports used lower cutoff points, such as BMI ³28, 25, or 24 kg/m². The overall quality of studies was good (mean Newcastle-Ottawa overall score, 6) with moderate risk of bias.

Pooled data showed that compared with normal weight women, those who were obese had worse disease-free survival (DFS) in all breast cancer subtypes: HR+HER2-BC (hazard ratio [HR], 1.26, 95 percent confidence interval [CI], 1.13–1.41; p<0.001), HER2+ BC (HR, 1.16, 95 percent CI, 1.06–1.26; p<0.001), and TNBC (HR, 1.17, 95 percent CI, 1.06–1.29; p=0.001).

Overall survival (OS) was likewise poor in obese versus nonobese women: HR+HER2-BC (HR, 1.39, 95 percent CI, 1.20–1.62; p<0.001), HER2+BC (HR, 1.18, 95 percent CI, 1.05–1.33; p=0.006), and TNBC (HR, 1.32, 95 percent CI, 1.13–1.53; p<0.001).

Meanwhile, overweight had a null effect on both DFS and OS in HER2+BC (p=0.85 and p=0.99, respectively) and TNBC (p=0.49 and p=0.17, respectively). In HR+HER2-BC, being overweight was associated with poorer OS (HR, 1.14, 95 percent CI, 1.07–1.22; p<0.001).